Motion measurement method, motion measurement system, and motion measurement program

BACKGROUND OF THE INVENTION

00011. Field of the Invention

0002The present invention relates to a method of measuring animal's motions made by activities of muscle fibers, a system for measuring the animal's motions, and a program enabling a computer to have functions for measuring the animal's motions.

00032. Related Background Art

0004There has been suggested a technology of measuring myoelectric signals generated in muscles of an animal including a human being and measuring a torque or the like of a joint of the animal based on the myoelectric signals (refer to, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2001-286451). According to the related art, the myoelectric signals are measured, first, with given forces produced in a motion region of a subject, the plurality of myoelectric signals measured are translated to a plurality of pseudo tensile forces, and then the maximum value among the plurality of pseudo tensile forces is determined as a normalized reference value. Subsequently, the myoelectric signals with the forces produced in the motion region of the subject are measured, pseudo tensile forces are acquired based on the measured myoelectric signals and the previously determined normalized reference value, and a torque is calculated based on the acquired pseudo tensile forces. The normalized reference value becomes the basis for identifying a correspondence between the myoelectric signals and the torque and for acquiring the torque based on the myoelectric signals in the motion region.

0005According to the related art, however, the myoelectric signals are measured under the condition where given forces are sequentially produced in a plurality of directions in the motion region by following the sequence in which consideration is given to muscle activation in the motion region, whereby the normalized reference value is determined. Therefore, in order to determine the normalized reference value to be a basis for measuring the torque, the related art forces the subject to produce the given forces sequentially in the plurality of directions in the motion region at least once. Furthermore, if the correspondence between the myoelectric signals and the torque varies with variations in various conditions such as an increase in muscular fatigue, the subject is forced to produce given forces in a plurality of directions in the motion region again in order to determine the normalized reference value anew. As mentioned above, according to the related art, the subject is forced to make a given motion different from a series of his/her motions concerned before or in the middle thereof.

0006For example, if the related art is adopted to a device for assisting a man in walking by giving a torque corresponding to a leg torque generated by a walking man bending and stretching his hip joints or knee joints, he is forced to make a motion different from the walking motion such as bending and stretching of his knees or standing on one foot before or during walking. On the other hand, a man using a walking aid device due to his weak muscle cannot make the given motion with the weak muscle even if he is forced to make it. Thus, he is very likely to have an uncomfortable feeling.

SUMMARY OF THE INVENTION

0007Therefore, it is an object of the present invention to provide a method, system, and program for accurately measuring a variable varying with animal's motions such as a joint torque in a series of the animal's motions.

0008According to one aspect of the present invention which achieves the object related to a method of measuring motions of an animal made by activities of muscle fibers, comprising the steps of: myoelectric potential measurement for measuring myoelectric potentials generated in an animal's body; first variable measurement for measuring a variable varying with the animal's motions; reference relational expression setting for setting a reference relational expression representing a relation between the myoelectric potentials and the variable on the basis of the myoelectric potentials measured in the myoelectric potential measurement step and the variable measured in the first variable measurement step; and second variable measurement for measuring a variable intended to be measured in the first variable measurement step on the basis of the myoelectric potentials measured in the myoelectric potential measurement step and according to the reference relational expression set in the reference relational expression setting step.

0009According to this aspect of the present invention, first the reference relational expression representing the relation between the myoelectric potentials and the variable is set in the reference relational expression setting step on the basis of the myoelectric potentials measured in the myoelectric potential measurement step and the variable measured in the first variable measurement step. This method does not force the animal to make a given motion to set the reference relational expression. Thereafter, the variable measured in the first variable measurement step is measured in the second variable measurement step on the basis of the myoelectric potentials measured in the myoelectric potential measurement step and according to the reference relational expression. For example, if the animal makes arbitrary first and second motions continuously, a reference relational expression is set on the basis of myoelectric potentials measured in the first motion and a variable corresponding to the first motion, first. Then, a variable corresponding to the second motion is measured according to the reference relational expression on the basis of the myoelectric potentials measured in the second motion.

0010Therefore, according to the aspect of the present invention, it is possible to measure the variable accurately in the series of animal's motions after setting the reference relational expression without forcing the animal to make a given motion.

0011Furthermore, the motion measurement method of the present invention has a feature that the first variable measurement step includes measuring the variable according to an inverse dynamics model representing a behavior of the animal.

0012According to the above feature, the variable is measured according to the inverse dynamics model representing the animal's behavior in the first variable measurement step.

0013Still further, the motion measurement method of the present invention further comprises a motion condition determination step of determining a motion condition of the animal on the basis of the variable varying with the animal's motions, wherein the first variable measurement step includes measuring the variable on the basis of the motion condition determined in the motion condition determination step.

0014According to the above feature, the variable is measured according to the animal's motion condition in the first variable measurement step.

0015Furthermore, the motion measurement method of the present invention further comprises a third variable measurement step of measuring the variable intended to be measured in the second variable measurement step simultaneously with and separately from the second variable measurement step and a deviation determination step of determining whether a deviation between the variable measured in the second variable measurement step and the variable measured in the third variable measurement step exceeds a threshold, wherein the reference relational expression setting step includes setting a new reference relational expression on the basis of the myoelectric potentials measured in the myoelectric potential measurement step and the variable measured in the third variable measurement step if the deviation is determined to exceed the threshold in the deviation determination step.

0016According to the above feature, the deviation determination step includes determining whether the deviation between the variable measured according to the reference relational expression in the second variable measurement step and the variable measured simultaneously with and separately from the second variable measurement step in the third variable measurement step exceeds the threshold. The “deviation” includes a deviation at a single time point and an average deviation, a cumulative deviation, and the like at a plurality of time points or for a continuous time. If the deviation is determined to exceed the threshold, the new reference relational expression is set on the basis of the myoelectric potentials and the variable measured in the third variable measurement step. If the deviation exceeds the threshold, it is estimated that the relation between the myoelectric potentials and the variable expressed by the reference relational expression diverges from an actual relation therebetween due to a change in condition such as muscular fatigue or perspiration. The setting of the new reference relational expression, however, avoids the divergence. Moreover, the setting of the new reference relational expression does not force the animal to make a given motion. Therefore, even in an occurrence of a change in condition such as muscular fatigue or perspiration, the variable can be accurately measured according to the reference relational expression accurately representing the relation between the myoelectric potentials and the variable without forcing the animal to make a given motion.

0017Still further, the motion measurement method of the present invention has a feature that the third variable measurement step includes measuring the variable in the same method as in the first variable measurement step.

0018According to this feature, the reference relational expression and the new reference relational expression can be set on the basis of the variable measured in the same method.

0019Still further, the motion measurement method of the present invention has a feature that the reference relational expression setting step includes setting an equation between a pseudo variable as a myoelectric potential function and the variable as a reference relational expression.

0020According to this feature, the variable is measured (calculated) by determining the pseudo variable as the myoelectric potential function according to the reference relational expression.

0021Furthermore, the motion measurement method of the present invention has a feature that the reference relational expression setting step includes setting the reference relational expression so that the maximum value of the pseudo variable equals the maximum value of the variable.

0022According to the foregoing features, the variable is measured (calculated) by determining the pseudo variable as the myoelectric potential function according to the reference relational expression. Furthermore, the variable is measured (calculated) by normalizing the pseudo variable so that the maximum value of the pseudo variable equals the maximum value of the variable. The “maximum value” of the variable and that of the pseudo variable include the maximum value of the variable and that of the pseudo variable in a given time span and the maximum value of the variable and that of the pseudo variable in each period if the variable and the pseudo variable change periodically.

0023Still further, the motion measurement method of the present invention has a feature that the first and second variable measurement steps each include measuring a torque produced in a body part of the animal as a variable.

0024According to this feature, the torque produced in the body part of the animal is measured as the variable.

0025According to another aspect of the present invention which achieves the object related to a system for measuring motions of an animal made by activities of muscle fibers, comprising: myoelectric potential measurement means for measuring myoelectric potentials generated in an animal's body; first variable measurement means for measuring a variable varying with the animal's motions; reference relational expression setting means for setting a reference relational expression representing a relation between the myoelectric potentials and the variable on the basis of the myoelectric potentials measured by the myoelectric potential measurement means and the variable measured by the first variable measurement means; and second variable measurement means for measuring a variable intended to be measured by the first variable measurement means on the basis of the myoelectric potentials measured by the myoelectric potential measurement means and according to the reference relational expression set by the reference relational expression setting means.

0026According to this aspect of the present invention, it is possible to accurately measure the variable in a series of the animal's motions after setting the reference relational expression without forcing the animal to make a given motion.

0027According to still another aspect of the present invention which achieves the object related to a program enabling a computer to process functions for measuring motions of an animal made by activities of muscle fibers, the program enabling the computer to process: a myoelectric potential measurement function of measuring myoelectric potentials generated in an animal's body; a first variable measurement function of measuring a variable varying with the animal's motions; a reference relational expression setting function of setting a reference relational expression representing a relation between the myoelectric potentials and the variable on the basis of the myoelectric potentials measured by the myoelectric potential measurement function and the variable measured by the first variable measurement function; and a second variable measurement function of measuring a variable intended to be measured by the first variable measurement function on the basis of the myoelectric potentials measured by the myoelectric potential measurement function and according to the reference relational expression set by the reference relational expression setting function.

0028According to this aspect of the present invention, the computer can be provided with a function of accurately measuring the variable in a series of the animal's motions after setting the reference relational expression without forcing the animal to make a given motion.

BRIEF DESCRIPTION OF THE DRAWINGS

0029<figref idref="DRAWINGS">FIG. 1</figref> is an explanatory configuration diagram showing a motion measurement system according to a first embodiment.

0030<figref idref="DRAWINGS">FIG. 2(</figref><i>a</i>) is an explanatory diagram showing myoelectric potential measurement using surface electrodes on the extensor side.

0031<figref idref="DRAWINGS">FIG. 2(</figref><i>b</i>) is an explanatory diagram showing myoelectric potential measurement using surface electrodes on the flexor side.

0032<figref idref="DRAWINGS">FIG. 3</figref> is an explanatory diagram showing a motion measurement method according to the first embodiment of the present invention.

0033<figref idref="DRAWINGS">FIG. 4</figref> is an explanatory diagram showing normalization of a pseudo variable with a variable in an ascending walking condition.

0034<figref idref="DRAWINGS">FIG. 5</figref> is an explanatory diagram showing normalization of a pseudo variable with a variable in a level walking condition.

0035<figref idref="DRAWINGS">FIG. 6</figref> is an explanatory configuration diagram of a motion measurement system according to a second embodiment of the present invention.

0036<figref idref="DRAWINGS">FIG. 7</figref> is an explanatory diagram showing a motion measurement method according to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0037The preferred embodiments of a motion measurement method, a motion measurement system, and a motion measurement program of the present invention will now be described in detail hereinafter with reference to the accompanying drawings.

0038<figref idref="DRAWINGS">FIG. 1</figref> shows an explanatory configuration diagram of a motion measurement system according to a first embodiment. <figref idref="DRAWINGS">FIGS. 2(</figref><i>a</i>) and <b>2</b>(<i>b</i>) show explanatory diagrams of a myoelectric potential measurement method. <figref idref="DRAWINGS">FIG. 3</figref> shows an explanatory diagram of a motion measurement method according to the first embodiment of the present invention. <figref idref="DRAWINGS">FIG. 4</figref> shows an explanatory diagram of normalization of a pseudo variable with a variable in an ascending walking condition. <figref idref="DRAWINGS">FIG. 5</figref> shows an explanatory diagram of normalization of a pseudo variable with a variable in a level walking condition. <figref idref="DRAWINGS">FIG. 6</figref> shows an explanatory configuration diagram of a motion measurement system according to a second embodiment of the present invention. <figref idref="DRAWINGS">FIG. 7</figref> shows an explanatory diagram of a motion measurement method according to the second embodiment of the present invention.

0039First, the motion measurement system according to the first embodiment of the present invention will be described by using <figref idref="DRAWINGS">FIGS. 1 to 5</figref>.

0040A motion measurement system <b>100</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> is for use in measuring motions of a human being (an animal). The motion measurement system <b>100</b> comprises a chest gyro sensor <b>101</b> for outputting a signal according to a tilt angular velocity of a human chest whose motions are to be measured, a chest fore-and-aft acceleration sensor <b>102</b> for outputting a signal corresponding to a fore-and-aft acceleration of the chest, a lumbar gyro sensor <b>103</b> for outputting a signal corresponding to a tilt angular velocity of a lumbar, a lumbar fore-and-aft acceleration sensor <b>104</b> for outputting a signal corresponding to a fore-and-aft acceleration of the lumbar, a lumbar vertical acceleration sensor <b>105</b> for outputting a signal corresponding to a vertical acceleration of the lumbar, a hip joint angle sensor <b>106</b> for outputting a signal corresponding to a flexion angle of a hip joint, and a knee joint angle sensor <b>107</b> for outputting a signal corresponding to a flexion angle of a knee joint.

0041The motion measurement system <b>100</b> includes a myoelectric potential measurement unit <b>110</b>, a first torque measurement unit (first variable measurement means) <b>120</b>, a reference relational expression setting unit <b>130</b>, and a second torque measurement unit (second variable measurement means) <b>140</b>. Each unit is formed by a microcomputer including a CPU, a ROM, a RAM, and the like as hardware and “a motion measurement program” of the present invention stored in a memory as software. The microcomputer, which is a part of each unit, operates using a battery <b>200</b> as a power supply. It contains the battery and is housed in a body-worn case <b>202</b>.

0042The myoelectric potential measurement unit <b>110</b> measures myoelectric potentials through surface electrodes <b>111</b> on the extensor side attached to regions of a medial vastus muscle, a lateral vastus muscle, and a musculus rectus femoris (extensor) on the surface of the human body as shown in <figref idref="DRAWINGS">FIG. 2(</figref><i>a</i>) and through surface electrodes <b>112</b> on the flexor side attached to regions of a semitendinosus muscle and a biceps femoris muscle (flexor) as shown in <figref idref="DRAWINGS">FIG. 2(</figref><i>b</i>). A first torque measurement unit <b>120</b> measures a knee joint torque by using an inverse dynamics model representing a human behavior on the basis of outputs from sensors <b>101</b> to <b>107</b>.

0043A reference relational expression setting unit <b>130</b> sets “a reference relational expression” representing a relation between the myoelectric potentials and the knee joint torque on the basis of the myoelectric potentials measured by the myoelectric potential measurement unit <b>110</b> and the knee joint torque measured by the first torque measurement unit <b>120</b>. Moreover, the reference relational expression setting unit <b>130</b> determines whether a deviation between the knee joint torque measured by the first torque measurement unit <b>120</b> and the knee joint torque measured by the second torque measurement unit <b>140</b> exceeds a threshold. If it determines that the deviation exceeds the threshold, it sets a new reference relational expression on the basis of the myoelectric potentials measured by the myoelectric potential measurement unit <b>110</b> and the knee joint torque measured by the first torque measurement unit <b>120</b>.

0044The second torque measurement unit <b>140</b> measures the knee joint torque on the basis of the myoelectric potentials measured by the myoelectric potential measurement unit <b>110</b> and according to the reference relational expression set by the reference relational expression setting unit <b>130</b>.

0045A motion measurement method executed by the motion measurement system <b>100</b> having the above configuration will be described below with reference to <figref idref="DRAWINGS">FIGS. 3 to 5</figref>. This motion measurement is started by switching an ON/OFF switch (not shown) attached to the case <b>202</b> from OFF to ON.

0046The myoelectric potential measurement unit <b>110</b> measures an extensor potential xi+ (i=1 (medial vastus muscle), 2 (lateral vastus muscle), 3 (musculus rectus femoris)) and a flexor potential xj− (j=1 (semitendinosus muscle), 2 (biceps femoris muscle)) through the surface electrodes <b>111</b> on the extensor side and the surface electrodes <b>112</b> on the flexor side (S<b>1</b>). The extensor potential xi+ and the flexor potential xj− are generated by activities of muscle fibers and vary with a human walking motion or the like. The extensor potential xi+ and the flexor potential xj− measured by the myoelectric potential measurement unit <b>110</b> are obtained by passing myoelectric signals, which have been detected by the surface electrodes <b>111</b> on the extensor side and the surface electrodes <b>112</b> on the flexor side, through a filter and an amplifier, A/D-converting the myoelectric signals, deriving absolute values therefrom, and passing them through a low-pass filter.

0047Furthermore, the first torque measurement unit <b>120</b> measures a knee joint torque T (corresponding to “a first variable measurement step” in S<b>2</b>) on the basis of outputs from the sensors <b>101</b> to <b>107</b> made by human motions and by using an inverse dynamics model representing a human behavior. Specifically, the first torque measurement unit <b>120</b> measures (estimates) the knee joint torque T on the basis of: a chest tilt angle and fore-and-aft acceleration; a lumber tilt angle, fore-and-aft acceleration, and vertical acceleration; a hip joint angle; and a knee joint angle. As for a concrete measurement method of the knee joint torque using the inverse dynamics model, for example, the method disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2003-89083 may be adopted, and its detailed description is omitted in this specification. The knee joint torque T is defined with the direction of extension of the knee joint, namely the direction of moving each lower leg forward, as a positive direction.

0048Furthermore, the reference relational expression setting unit <b>130</b> sets a reference relational expression between the extensor potential xi+ and the flexor potential xj− measured by the myoelectric potential measurement unit <b>110</b> and the knee joint torque T measured by the first torque measurement unit <b>120</b> for each motion condition determined by the motion condition determination unit <b>150</b> (S<b>3</b>).

0049Specifically, as expressed by the following equation (1), an equation between the knee joint torque T measured using the inverse dynamics model by the first torque measurement unit <b>120</b> and a pseudo torque T′ as a function of the extensor potential x+ and the flexor potential x− measured by the myoelectric potential measurement unit <b>110</b> is set as a reference relational expression: <br /><i>T=T</i>′(<i>xi+, xj</i>−)  (1)

0050The pseudo torque T′ as the function of the extensor potential x+ and the flexor potential x− is defined by the following equation (2): <br /><i>T′=Σi=</i>1 to 3<i>ci+xi+MAi++Σi=</i>1, 2<i>cj−xj−MAj−</i>  (2)<br /> where ci+ and cj− are coefficients having signs reversed from each other, wherein a ratio between them is set, for example, as expressed by ci+:cj−=1:−⅓; and MAi+ is a moment arm of the extensor, namely a distance between a rotation center of the joint and a position where the extensor adheres to a bone, varying with the flexion angle of the joint. Likewise, MAj− is a moment arm of the flexor, namely a distance between a rotation center of the joint and a position where the flexor adheres to a bone, varying with the flexion angle of the joint. The extensor moment arm MAi+ and the flexor moment arm MAj− may be assumed to be equal to each other.

0051The coefficients ci+ and cj− are determined so that the maximum value Tmax of the knee joint torque T measured by the first torque measurement unit <b>120</b> equals the maximum value Tmax′ of the pseudo torque T′. This normalizes (changes in scale) the pseudo torque T′ so that the maximum value Tmax of the knee joint toque T (indicated by a solid line) equals the maximum value Tmax′ of the pseudo torque (indicated by a dashed line), for example, as shown in <figref idref="DRAWINGS">FIG. 4</figref> and <figref idref="DRAWINGS">FIG. 5</figref>. <figref idref="DRAWINGS">FIG. 4</figref> shows a joint torque T (solid line) and a normalized pseudo torque (dashed line) T′ in “an ascending walking condition” in which a man is walking up stairs or a slope. <figref idref="DRAWINGS">FIG. 5</figref> shows a joint torque T (solid line) and a normalized pseudo torque (dashed line) T′ in “a level walking condition” in which a man is walking on level ground.

0052If an extensor potential x+ is measured for one of a plurality of extensors and a flexor potential x− is measured for one of a plurality of flexors, the pseudo torque T′ may be defined by the following equation (3): <br /><i>T′=c+x+MA++c−x−MA−</i>  (3)

0053If myoelectric potentials are measured for one extensor and a plurality of flexors or vice versa, the pseudo torque T′ may be defined by the following equations (4) and (5): <br /><i>T′=Σici+xi+MAi++c−x−MA−</i>  (4)<br /><i>T′=c+x+MA++Σjcj−xj−MAj−</i>  (5)

0054Thereafter, the myoelectric potential measurement unit <b>110</b> measures the extensor potential xi+ and the flexor potential xj− (S<b>4</b>). Then, the second torque measurement unit <b>140</b> measures the knee joint torque T on the basis of the extensor potential x+ and the flexor potential x− measured by the myoelectric potential measurement unit <b>110</b> and according to the reference relational expression corresponding to the motion condition determined by the reference relational expression setting unit <b>130</b> (see the equations (1) and (2)) (S<b>5</b>; corresponds to “a second variable measurement step”).

0055Furthermore, the first torque measurement unit <b>120</b> measures the knee joint torque T by using the inverse dynamics model on the basis of outputs from the sensors <b>101</b> to <b>107</b> (S<b>6</b>; corresponds to a third variable measurement step).

0056Moreover, the reference relational expression setting unit <b>130</b> determines whether the deviation δT between the knee joint torque T (S<b>5</b>) measured by the second torque measurement unit <b>140</b> and the knee joint torque T (S<b>6</b>) measured by the first torque measurement unit <b>120</b> exceeds a threshold E or not (S<b>7</b>; corresponds to a deviation determination step). The deviation δT may be either a deviation between the maximum values of the both knee joint torques or an average deviation or a cumulative deviation for a certain period of time of the both knee joint torques.

0057If the reference relational expression setting unit <b>130</b> determines that the deviation δT exceeds the threshold ε (NO in S<b>7</b>), it sets a new reference relational expression (S<b>3</b>) by resetting the coefficients ci+ and cj− of the equation (2) on the basis of the knee joint torque T measured by using the inverse dynamics model (S<b>6</b>) and the extensor potential xi+ and the flexor potential xj− measured by the myoelectric potential measurement unit <b>110</b> (S<b>4</b>). Thereafter, the second torque measurement unit <b>140</b> measures the knee joint torque T according to the new reference relational expression (S<b>5</b>).

0058On the other hand, if the reference relational expression setting unit <b>130</b> determines that the deviation δT does not exceed the threshold ε (YES in S<b>7</b>) and the ON/OFF switch (not shown) remains to be set on (ON in S<b>8</b>), it does not set the new reference relational expression. In this condition, the second torque measurement unit <b>140</b> measures the knee joint torque T according to the existing reference relational expression (S<b>5</b>). If the ON/OFF switch is set off (OFF in S<b>8</b>), the subsequent processing such as myoelectric potential measurement or knee joint torque measurement is terminated.

0059According to the motion measurement method executed by the motion measurement system <b>100</b>, for example, if a human being (animal) makes arbitrary first and second motions continuously, a reference relational expression is set on the basis of myoelectric potentials (xi+ and xj−) measured in the first motion and the knee joint torque (variable) T corresponding to the first motion (S<b>1</b> to S<b>3</b>), first. Then, the knee joint torque T corresponding to the second motion is measured according to the reference relational expression on the basis of myoelectric potentials (xi+ and xj−) measured in the second motion following the first motion (S<b>4</b> and S<b>5</b>).

0060Therefore, it is possible to accurately measure the knee joint torque T in a series of motions of a human being (animal) after setting the reference relational expression without forcing the human being to make a given motion.

0061If the deviation δT between the knee joint torque T (S<b>5</b>) measured according to the reference relational expression and the knee joint torque T (S<b>6</b>) measured simultaneously with and separately therefrom exceeds the threshold ε (NO in S<b>7</b>), a new reference relational expression is set (S<b>3</b>) on the basis of the myoelectric potentials (S<b>4</b>) and the knee joint torque T (S<b>6</b>).

0062If the deviation δT exceeds the threshold ε, it is estimated that the relation between the myoelectric potentials (xi+ and xj−) and the knee joint torque T represented by the reference relational expression diverges from an actual relation therebetween due to a change in condition such as muscular fatigue or perspiration. The setting of the new reference relational expression, however, avoids the divergence. In addition, the human being is not forced to make a given motion to set the new reference relational expression. Therefore, even if a change in condition such as muscular fatigue or perspiration occurs, it is possible to measure the knee joint torque T accurately according to the reference relational expression accurately representing the relation between the myoelectric potentials (xi+ and xj−) and the knee joint torque T without forcing the human being to make a given motion.

0063The following describes a motion measurement system according to a second embodiment of the present invention with reference to <figref idref="DRAWINGS">FIG. 6</figref> and <figref idref="DRAWINGS">FIG. 7</figref>.

0064A configuration of the motion measurement system of the second embodiment of the present invention will now be described with reference to <figref idref="DRAWINGS">FIG. 6</figref>. A motion measurement system <b>100</b> of the second embodiment shown in <figref idref="DRAWINGS">FIG. 6</figref> does not include the chest gyro sensor <b>101</b>, the chest fore-and-aft acceleration sensor <b>102</b>, the lumbar gyro sensor <b>103</b>, the lumbar fore-and-aft acceleration sensor <b>104</b>, and the lumbar vertical acceleration sensor <b>105</b>. On the other hand, it is the same in the configuration as the motion measurement system of the first embodiment shown in <figref idref="DRAWINGS">FIG. 1</figref> and <figref idref="DRAWINGS">FIG. 2</figref> except that it additionally includes a motion condition determination unit <b>150</b>. Therefore, the same reference numerals are retained for the same parts and their description is omitted here.

0065The motion condition determination unit <b>150</b> determines a human motion condition on the basis of an output from a hip joint angle sensor <b>106</b> and an output from a knee joint angle sensor <b>107</b>.

0066A motion measurement method executed by the motion measurement system <b>100</b> having the foregoing configuration will be described by using <figref idref="DRAWINGS">FIG. 7</figref>. The motion measurement method of the second embodiment is substantially the same as the motion measurement method of the first embodiment except that a motion condition determined by the motion condition determination unit <b>150</b> is used instead of the inverse dynamics model in “the measurement of the knee joint torque T” in the first and third variable measurement steps.

0067A myoelectric potential measurement unit <b>110</b> measures an extensor potential xi+ and a flexor potential xj− through surface electrodes <b>111</b> on the extensor side and surface electrodes <b>112</b> on the flexor side (S<b>21</b>).

0068Moreover, the motion condition determination unit <b>150</b> measures a human motion condition on the basis of outputs from the hip joint angle sensor <b>106</b> and the knee joint angle sensor <b>107</b> (S<b>22</b>). As for a concrete determination method of the motion condition, for example, the method disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2003-116893 may be adopted, and its detailed description is omitted in this specification. By using the method, the motion condition determination unit <b>150</b> determines which human motion condition is applicable out of a plurality of motion conditions such as “a level walking condition” in which a man is walking on a level ground or a vanishingly gentle slope, “a descending walking condition” in which he is walking down stairs or a slope, “an ascending walking condition” in which he is walking up stairs or a slope, “a rising-from-chair condition” in which he is rising from a chair, and “a sitting-on-chair condition” in which he is sitting on a chair from the stand up position.

0069Furthermore, the first torque measurement unit <b>120</b> reads out (measures) a knee joint torque T stored in a memory (not shown) according to the corresponding motion condition on the basis of the motion condition determined by the motion condition determination unit <b>150</b> (S<b>23</b>; corresponds to “a first variable measurement step”). For example, if the motion condition determination unit <b>150</b> determines the condition to be “the ascending walking condition,” the first torque measurement unit <b>120</b> reads out (measures) a knee joint torque T, as indicated by a solid line in <figref idref="DRAWINGS">FIG. 4</figref>, previously stored in the memory so as to correspond to the ascending walking condition. If the motion condition determination unit <b>150</b> determines the condition to be “the level walking condition,” the first torque measurement unit <b>120</b> reads out (measures) a knee joint torque T, as indicated by a solid line in <figref idref="DRAWINGS">FIG. 5</figref>, previously stored in the memory so as to correspond to the level walking condition.

0070In addition, the reference relational expression setting unit <b>130</b> sets a reference relational expression between the extensor potential xi+ and the flexor potential xj− measured by the myoelectric potential measurement unit <b>110</b> and the knee joint torque T measured by the first torque measurement unit <b>120</b> for each motion condition determined by the motion condition determination unit <b>150</b> (S<b>24</b>).

0071Thereafter, the myoelectric potential measurement unit <b>110</b> measures the extensor potential xi+ and the flexor potential xj− (S<b>25</b>). Then, the second torque measurement unit <b>140</b> measures the knee joint torque T on the basis of the extensor potential x+ and the flexor potential x− measured by the myoelectric potential measurement unit <b>110</b> and according to the reference relational expression corresponding to the motion condition determined by the reference relational expression setting unit <b>130</b> (S<b>26</b>; corresponds to “a second variable measurement step”).

0072The motion condition determination unit <b>150</b> determines the user motion condition on the basis of outputs from the hip joint angle sensor <b>106</b> and the knee joint angle sensor <b>107</b> (S<b>27</b>). Furthermore, the first torque measurement unit <b>120</b> reads out (measures) the knee joint torque T stored in the memory (not shown) on the basis of the motion condition determined by the motion condition determination unit <b>150</b> corresponding to the motion condition (S<b>28</b>; corresponds to “a third variable measurement step”).

0073The reference relational expression setting unit <b>130</b> determines whether the deviation δT between the knee joint torque T (S<b>26</b>) measured by the second torque measurement unit <b>140</b> and the knee joint torque T (S<b>28</b>) measured by the first torque measurement unit <b>120</b> exceeds the threshold ε (S<b>29</b>; corresponds to “a deviation determination step”).

0074If the reference relational expression setting unit <b>130</b> determines that the deviation δT exceeds the threshold ε (NO in S<b>29</b>), it sets a new reference relational expression (S<b>24</b>) by resetting the coefficients ci+ and cj− in the equation (2) on the basis of the knee joint torque T (S<b>28</b>) and the extensor potential xi+ and the flexor potential xj− (S<b>25</b>) measured by the myoelectric potential measurement unit <b>110</b>. Thereafter, the second torque measurement unit <b>140</b> measures the knee joint torque T according to the new reference relational expression (S<b>26</b>).

0075On the other hand, if the reference relational expression setting unit <b>130</b> determines that the deviation δT does not exceed the threshold ε (YES in S<b>29</b>) and the ON/OFF switch (not shown) remains to be set on (ON in S<b>30</b>), it does not set a new reference relational expression. In this condition, the second torque measurement unit <b>140</b> measures the knee joint torque T according to the existing reference relational expression (S<b>26</b>). If the ON/OFF switch is set off (OFF in S<b>30</b>), the subsequent processing such as myoelectric potential measurement or knee joint torque measurement is terminated.

0076According to the motion measurement method executed by the motion measurement system <b>100</b>, it is also possible to accurately measure the knee joint torque T in a series of motions of a human being (animal) after setting the reference relational expression without forcing the human being to make a given motion. Moreover, in case of a change in condition such as muscular fatigue or perspiration, the knee joint torque T can be accurately measured according to the reference relational expression accurately representing the relation between the myoelectric potentials (xi+ and xj−) and the knee joint torque T without forcing the human being to make a given motion.

0077While the animal whose motions are measured has been a human being in the above embodiments, it can be any of all kinds of animals that make motions with activities of muscle fibers such as a monkey, a giraffe, or any other mammal or a fish as an alternative.

0078While the knee joint torque has been measured as a variable in the above embodiments, the variable to be measured may be a joint torque other than the knee joint torque, such as a hip joint torque, an ankle joint torque, a cubital joint torque, and a shoulder joint torque, or a joint angle, a joint angular velocity, a joint angular acceleration, and a rate of change in joint torque of a knee joint or the like as an alternative.

0079While the joint torque has been measured by using the inverse dynamics model on the basis of the output from the knee joint angle sensor <b>107</b> in the first embodiment and the joint torque has been measured on the basis of the motion condition determined based on the output from the knee joint angle sensor <b>107</b> in the second embodiment, the variable of the joint torque or the like may be measured in various methods such as, for example, in which a computer (not shown) measures the variable such as the joint torque on the basis of an after image of a camera (not shown) after the camera images human behaviors as an alternative.

0080While the coefficients ci+ and cj− of the reference relational expression (See the equations (1) and (2)) have been determined so that the maximum value Tmax of the torque T equals the maximum value Tmax′ of the pseudo torque T′ in the above embodiment, the coefficients ci+ and cj− of the reference relational expression may be determined so as to minimize an average deviation or a cumulative deviation at a plurality of time points or for a certain period of time of the torque T and the pseudo torque T′ as an alternative.

0081While the torque (variable) measurement method in the first variable measurement step (S<b>2</b> in <figref idref="DRAWINGS">FIG. 3</figref> and S<b>23</b> in <figref idref="DRAWINGS">FIG. 7</figref>) is identical with that in the third variable measurement step (S<b>6</b> in <figref idref="DRAWINGS">FIG. 3</figref> and S<b>26</b> in <figref idref="DRAWINGS">FIG. 7</figref>) in the above embodiments, the torque measurement methods in the both steps may be different from each other as an alternative.

0082In the second embodiment, the coefficients ci+ and cj− (see the equations (1) and (2)) and thus the reference relational expression may be set according to the motion condition determined by the motion condition determination unit <b>150</b>. According to this embodiment, the torque or other variables can be more accurately measured according to the optimum reference relational expression corresponding to a user's (human being's) motion condition.